A couple questions (precal)

1. The base of an isosceles triangle is half as long as the two equal sides. Write the area of the triangle as a function of the length of the shorter leg.

I've already gotten pretty far on this one.
X is the base, H is the height. 2x is the side lengths because its twice the base
1/2(x)*(h)= area
h^2+ (1/2x)^2=(2x)^2
h^2+1/4x^2= 4x^2
this is where i get lost...
My teacher told me it goes to
sqrt of h^2 = sqrt 15/16x^2
then it goes to h=sqrt15 divided by 4x
then you just plug that is. Could you tell me how it becomes sqrt of 15/16 x^2?

2.A sphere inside a cube, tangent to all six faces. Find the surface area of the cube as a function of the radius of the sphere.

The base of an isosceles triangle is half as long as the two equal sides. Write the area of the triangle as a function of the length of the shorter leg.

I've already gotten pretty far on this one.
X is the base, H is the height. 2x is the side lengths because its twice the base
1/2(x)*(h)= area
h^2+ (1/2x)^2=(2x)^2
h^2+1/4x^2= 4x^2
this is where i get lost...
My teacher told me it goes to
sqrt of h^2 = sqrt 15/16x^2
then it goes to h=sqrt15 divided by 4x
then you just plug that is. Could you tell me how it becomes sqrt of 15/16 x^2?